Taipei, Taiwan — The dozens of pilots who operate TransAsia Airways' ATR propeller-jets began proficiency tests on Saturday, three days after one of the carrier's ATRs crashed into a river, killing at least 40 people.

The airline said it had canceled 90 flights over the next three days to accommodate the requirement by Taiwan's Civil Aeronautics Administration that all 71 of its ATR pilots be retested.

Preliminary investigations indicate the pilots of Wednesday's doomed flight shut off a running engine of the ATR 72 after its other engine went idle, a move that aviation experts said was an error.

"It's a mistake," said John M. Cox, a former US Airways pilot and now head of a safety-consulting company. "There are procedures that pilots go through — safeguards — when you're going to shut down an engine, particularly close to the ground. Why that didn't occur here, I don't know."

Local prosecutors have said they will look into the possibility of "professional error."

Thomas Wang, head of Taiwan's Aviation Safety Council, said Saturday that it was too early to reach conclusions about any pilot error.

Pratt & Whitney Canada, the plane's engine maker, and the safety council have begun to examine both of the aircraft's engines, a process that can take four months, Wang said.

The crash into the muddy Keelung River in Taipei minutes after takeoff killed at least 40 of the 58 people who were aboard the plane, with rescuers recovering five more bodies on Saturday, according to the Taipei City Fire Department. Three people remain missing.

Fifteen people were rescued with injuries after the accident, which was captured in a dramatic dashboard camera video that showed the aircraft banking steeply and scraping a highway overpass before it hurtled into the water.

With warmer temperatures, divers on Saturday were able to retrieve more bodies, which were found hundreds of meters downriver from the crash site.

One body turned up near the shore, and others were submerged in mud, said You Chia-yi, a command post chief with the fire department.

Family members of those still missing have given up hope, said Lee Hung Shu-ying, a Tzu Chi Foundation volunteer who talked to numerous relatives Saturday.

"They know it's not possible (to survive) with the weather being so cold," she said. "They just hope the bodies can be found."